1. Field of the Invention
The present invention relates to an ink-jet recording apparatus and ink-jet recording method, for recording images on a recording medium using ink containing color material and a liquid essentially containing no color material.
2. Description of the Related Art
As photocopiers, word processors, computers and other information processing equipment, and communication devices come into common use, ink-jet recording apparatuses are rapidly becoming commonplace as one type of output device thereof, for performing recording of digital images using the ink-jet method. With such recording apparatuses, recording heads made up of multiple ink discharging nozzles in integrated arrays with multiple ink discharge openings and liquid channels are used to improve recording speed, and further, in recent years, arrangements containing a plurality of such recording heads are often used to deal with color which is becoming commonplace.
The ink-jet recording method performs recording of dots by forming flying droplets of ink as the recording liquid and landing these on a recording medium such as paper or the like, and has a low noise factor due to being a non-contact method. Also, high resolution and high-speed recording is enabled by the increased density of the ink discharge nozzles. Further, no special processing such as developing or fixing is necessary for recording media such as plain paper or the like, so high-quality images can be obtained at low cost. Accordingly, this method has become widespread in recent years. Particularly, on-demand type ink-jet recording apparatuses can be easily arranged to deal with color, and further the apparatus itself can be easily reduced in size and complexity, so the demand thereof in the future is expected to be great. Also, as such color becomes commonplace, even higher image quality and speed are being required.
In the present state of such high image quality being required, there are various methods being proposed regarding improving image quality. One method for improving image quality involves making the droplets of discharged ink smaller. Reducing the diameter of the nozzles is the most effective method for reducing the size of the droplets, and improved image quality is achieved by arraying the ink discharging nozzles with small nozzle diameters in high density. The reason that reducing the size of the discharged ink droplets leads to higher image quality is that the dots are not as conspicuous, and the number of gradients which can be represented without increasing the matrix size of one pixel can be increased. In other words, reducing the size of the discharged ink droplets enables the number of gradients to be increased without losing resolution. Incidentally, the higher the density of the arrayed nozzles is, the higher the output resolution is, but there is a limit to how high the density can be, due to restrictions in the manufacturing process. This is also true for reducing the size of the discharged ink droplets, and currently, due to restrictions in the manufacturing process, the limit on how little the amount discharged can be is 1 to several picoliters (several nanograms), and 20 to 40 xcexcm recorded dot diameters on the recording medium.
Also, as another method for improving image quality, there is a method of using concentration ink which is ink of the same color in different ink concentrations. With this method, highlight portions (portions with low concentration) are recorded with low-concentration ink so as to make the grainy appearance of the recording dots less conspicuous. This also enables a great number of gradients to be represented, by using ink with low and high concentration according to the gradients. Thus, using ink with low and high concentration enables high-quality images. Also, as another method for making the grainy appearance of the recording dots less conspicuous in highlight portions, Japanese Patent Laid-Open No. 59-115853 discloses a method wherein transparent ink is recorded over the recorded dots so as to thin the concentration of the recorded dots and represent an overall light color. According to this Japanese Patent Laid-Open No. 59-115853, the number of gradients represented is not being increased, but the grainy appearance in the highlight portions is reduced, ultimately leading to high quality.
Also, as another method for improving image quality, there is a method wherein the size of the recording dots is controlled by pulse modulation, thereby increasing the number of gradients which can be represented. This is a method wherein the dot recording area is changed per unit area by changing the diameter of the dots, thereby changing the apparent concentration, and consequently representing gradients.
Also, there are methods for high quality images other than recording images with gradation (i.e., wherein the gradient level is not constant) with high quality, i.e., methods aiming to improve the quality of characters. As one method for such improvement in character quality, there is edge enhancing wherein the edge portions of characters are enhanced. For example, Japanese Patent Laid-Open No. 1-212176 discloses a method wherein image signals are subjected to secondary differentiation and computation is performed with original image signals and smoothed data, thereby enhancing the edge portions. Also, Japanese Patent Laid-Open No. 8-72236 discloses a method wherein the amount of ink discharged at the edge portions is greater than the non-edge portions, thereby raising the concentration at the edge portions. Performing such edge enhancing allows characters with clear outlines to be formed.
Though various methods are being proposed for realizing high image quality as described above, these methods have various problems, as described below.
{circle around (1)} Reducing the size of discharged ink droplets increases the resolution, but the area covered by each ink dot is reduced. This means that the number of ink dots necessary for covering a certain area on the recording medium increases, leading to reduction in printing speed. That is to say, reducing the size of the discharged ink droplets contributes to high image quality but contradicts high speed.
{circle around (2)} Arraying ink discharge nozzles with reduced nozzle diameters in high density allows the number of gradients to be increased without losing resolution as described above, but indiscriminately increasing the density of nozzles does not necessarily mean that high image quality can be realized. The reason is that an excessively high density array of nozzles leads to adjacent ink dots on the recording medium overlapping unnecessarily, which may cause the ink dots to blur. Such blurring causes deterioration in image quality. Also, the ink-jet method has a phenomena called ink shifting, and there is a problem in that this ink shifting becomes more pronounced as the density of the nozzles is increased and the resolution is raised. Consequently, this ink shifting leads to deterioration in image quality.
{circle around (3)} An arrangement may be conceived wherein adjacent nozzles do not simultaneously discharge ink such that ink is not overlapped in the same main scan of the recording head, thereby reducing image deterioration due to the blurring and ink shifting described above in problem {circle around (2)}. For example, in the event that there are 256 nozzles, each nozzles rests intermittently, so that 128 nozzles are driven to record the image with each scan. With such an arrangement, in the event that a solid image is recorded, the printing duty of one main scan of the recording head is 50%, so the printing concentration of one main scan of the recording head deteriorates. On the other hand, an arrangement may be conceived wherein the recording head performs two main scans to avoid deterioration of the printing concentration, but this would make the recording time longer.
{circle around (4)} In the event of using concentration ink, a recording head and ink cartridge are provided for each ink to be used, so the number of recording heads and the number of ink cartridges increases, meaning that the size of the recording apparatus increases, as well. For example, in the event of using ink of the seven colors of yellow, magenta, cyan, black, light magenta, light cyan, and light yellow, a head width for several colors is required. Also, an increase in the number of recording heads and carriages means an increase in weight accordingly, and the load for driving the carriages increases, so there arises the need to use a driving motor with more torque, and the need for complex mechanisms to maintain capping capabilities of the multiple caps provided according to the number of recording heads, thereby increasing costs.
{circle around (5)} Also, in the event of using concentration ink, in the event that the difference in concentration between the high concentration ink and low concentration ink is great, gradient reproduction at the switchover portion (border portion) between the high concentration ink and low concentration ink on the recorded image is not linear, which tends to cause pseudo outlines. Also, changes in the grainy characteristics and changes of tone in the recorded image occur at the above ink switchover portion, making an unnatural-looking image. In other words, the gradient becomes non-continuous due to the difference in concentration between the high concentration ink and low concentration ink. There is a method to solve this problem, which involves increasing the number of gradient concentrations, such as using a low-concentration ink, mid-concentration ink, and high-concentration ink, to perform recording, but it is clear that this would magnify the above problems regarding increased size.
{circle around (6)} With some ink-jet recording apparatuses using concentration ink, there are cases wherein the four colors of yellow, magenta, cyan, and black are used in the normal mode wherein characters, charts, etc., are recorded, and the six colors of yellow, magenta, cyan, light magenta, light cyan, and light yellow are used in the high-quality image mode wherein photographic image quality images and the like are recorded. In such cases, the black ink cartridge and the light ink cartridge are exchanged, but such cartridge exchanging is a problem in that it is troublesome for the user.
{circle around (7)} In the event of representing gradients by the dot diameter control method, the amount of ink discharge must be controlled in order to keep the dot diameter to the desired size, but it is difficult to control the amount of ink discharge with this method, and so there is the problem that this method has poor gradient reproducibility.
In this way, there are various problems such as the above-described problems {circle around (1)} through {circle around (7)} regarding conventional attempts to increase the image quality. What is necessary for ink-jet recording apparatuses from now on, in addition to further improvements in image quality, is realization of increased speed, reduced costs, reduction in size of the apparatus, and so forth. In order to realize such, various problems such as the above-described problems {circle around (1)} through {circle around (7)} must be solved.
Also, from the above problems {circle around (1)} through {circle around (7)}, it is apparent that a high-density array of ink discharging nozzles having small nozzle diameters alone has great difficulties in realizing high image quality and high speed. In order to obtain higher image quality, it is important that either the discharged ink droplets which have been reduced in size must be made to land on the recording medium with high precision, or that even in the event that there is ink shifting this must be made to be inconspicuous. Also, for high-speed recording, the printing duty for one main scan of the recording head must be raised, but in the event that the density of the nozzles is too high the ink shifting becomes distinct, which is undesirable.
Also, though the above description mainly deals with the quality of picture images with gradation (i.e., wherein the gradient level is not constant), realizing high quality must also take into consideration the quality of images such as characters, lines, charts, posters, etc., with no gradation (i.e., wherein the gradient level is constant), besides picture images. That is, an arrangement may be conceived wherein edge enhancing is applied to images of characters, lines, charts, posters, etc., so as to form a sharp and clear image. However, with the edge enhancing method disclosed in Japanese Patent Laid-Open No. 8-72236, the amount of ink discharged at the edge portion is increased, so it is conceivable that the edge portion will blur. Consequently, a sharp edge portion cannot be formed. Also, with conventional arrangements for improving the image quality with edge enhancing, recording time has not been taken into consideration. For example, in the event that the amount of ink discharged at the edge portion is increased to improve the image quality, performing the recording with one pass will result in adjacent dots blurring one another, so there is the need to record with multi-passes. This results in extra time consumed, which is unfavorable. Also, in the event of recording characters for posters and the like, the large characters of posters take time to fill in. This means that even if the edge portion could be recorded in a short time, the recording time for the overall image is long, which is unfavorable. Accordingly, thought must be given not only to the edge portion alone but also to the recording method for the non-edge portion. Thus, conventional arrangements have attempted to improve image quality by edge enhancing, but did not focus on high speeds.
From the above, an arrangement is awaited which is capable of recording picture images with high resolution and a great number of gradients, which improves image quality by recording images such as characters, lines, charts, posters, etc., with clarity, and further records picture images and images such as characters, lines, charts, posters, etc., at high speed.
The present invention has been made in light of the above objects, and accordingly, it is an object thereof to provide an ink-jet recording apparatus and recording method wherein both high image quality and high speed have been realized, using a recording head wherein nozzles with small diameter have been arrayed in high density.
Also, another object of the present invention is to provide an ink-jet recording apparatus and recording method wherein smooth gradation can be represented by increasing intermediate gradients without lowering output resolution, and also capable of reducing the grainy appearance at highlight portions.
Further, another object of the present invention is to provide an ink-jet recording apparatus and recording method wherein high quality and high speed can be realized without incurring enlarging of the apparatus or increased costs.
Further yet, another object of the present invention is to provide an ink-jet recording apparatus and recording method capable of forming images such as characters, lines, charts, posters, etc., with sharp edge portions, in a short time.
Moreover, another object of the present invention is to provide an ink-jet recording apparatus and recording method capable of recording picture areas at high resolution and with a great number of gradients, and also to reduce the grainy appearance in highlight portions.
To this end, the ink-jet recording method according to the present invention is configured as follows.
That is, an ink-jet recording method which uses a recording head having a nozzle array comprised of at least one ink discharging nozzle for discharging ink which contains color material and at least one liquid discharging nozzle for discharging a liquid which essentially does not contain color material being alternately adjacently arrayed in a predetermined direction, and the ink and the liquid being discharged on a recording medium while relatively scanning the recording head and the recording medium, thereby recording an image, comprises the steps of:
a determining step for determining whether to record at least one area of the image to be recorded with the ink alone, or to record the area with both the ink and the liquid; and
a recording step for performing the recording of the above area based on the determined results of the determining step;
wherein, in the event of recording the area with both the ink and the liquid, in the recording step the ink discharged from a predetermined ink discharging nozzle and the liquid discharged from a predetermined liquid discharging nozzle adjacent to the predetermined ink discharging nozzle each land at different positions on the recording medium, and the landed ink and the landed liquid come into contact on the recording medium.
Also, the ink-jet recording apparatus according to the present invention is configured as follows.
That is, an ink-jet recording apparatus which uses a recording head having a nozzle array comprised of at least one ink discharging nozzle for discharging ink which contains color material and at least one liquid discharging nozzle for discharging a liquid which essentially does not contain color material being alternately adjacently arrayed in a predetermined direction, and the ink and the liquid being discharged on a recording medium while relatively scanning the recording head and the recording medium, thereby recording an image, comprises:
determining means for determining whether to record at least one area of the image to be recorded with the ink alone, or to record the area with both the ink and the liquid; and
recording control means for controlling the recording head such that recording is performed based on the determined results by the determining means;
wherein, in the event of recording the area with both the ink and the liquid, in recording the ink discharged from a predetermined ink discharging nozzle and the liquid discharged from a predetermined liquid discharging nozzle adjacent to the predetermined ink discharging nozzle each land at different positions on the recording medium, and the landed ink and the landed liquid come into contact on the recording medium.
Also, the computer-readable storage medium according to the present invention is configured as follows.
That is, a computer-readable storage medium stores a program for executing the recording control step for an ink-jet recording apparatus which uses a recording head having a nozzle array comprised of at least one ink discharging nozzle for discharging ink which contains color material and at least one liquid discharging nozzle for discharging a liquid which essentially does not contain color material being alternately adjacently arrayed in a predetermined direction, and the ink and the liquid being discharged on a recording medium while relatively scanning the recording head and the recording medium, thereby recording an image, the program comprising:
a determining step for determining whether to record at least one area of the image to be recorded with the ink alone, or to record the area with both the ink and the liquid; and
a generating step for generating recording data based on the determined results of the determining step;
wherein, in the event of determining recording of the area with both the ink and the liquid, the generating of the recording data in the generating step is executed such that the ink discharged from a predetermined ink discharging nozzle and the liquid discharged from a predetermined liquid discharging nozzle adjacent to the predetermined ink discharging nozzle each land at different positions on the recording medium, and the landed ink and the landed liquid come into contact on the recording medium.
Also, the program according to the present invention is configured as follows.
That is, a program for controlling an ink-jet recording apparatus which uses a recording head having a nozzle array comprised of at least one ink discharging nozzle for discharging ink which contains color material and at least one liquid discharging nozzle for discharging a liquid which essentially does not contain color material being alternately adjacently arrayed in a predetermined direction, and the ink and the liquid being discharged on a recording medium while relatively scanning the recording head and the recording medium, thereby recording an image, comprises:
a determining step for determining whether to record at least one area of the image to be recorded with the ink alone, or to record the area with both the ink and the liquid; and
a generating step for generating recording data based on the determined results of the determining step;
wherein, in the event of determining recording of the area with both the ink and the liquid, the generating of the recording data in the generating step is executed such that the ink discharged from a predetermined ink discharging nozzle and the liquid discharged from a predetermined liquid discharging nozzle adjacent to the predetermined ink discharging nozzle each land at different positions on the recording medium, and the landed ink and the landed liquid come into contact on the recording medium.
Note that in the present specification, the term xe2x80x9crecording inkxe2x80x9d refers to ink which contains color material. Also, xe2x80x9cclear inkxe2x80x9d refers to liquid which essentially does not contain color material, e.g., a liquid consisting of the components remaining after the color material component has been removed from the above recording ink.
Also, note that in the present specification, a head with a nozzle pitch of 1/x inches is referred to as an xe2x80x9cx dpi headxe2x80x9d. For example, in the event that the nozzle pitch is {fraction (1/1200)} inches, this is a 1200 dpi head.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.